The dry season in the Brazilian Amazon is becoming more severe, and the forest’s temperature rose 2 degrees between 1985 and 2020, according to a study led by scientists from the University of São Paulo.
The analysis reviewed 35 years of data on deforestation, temperature, and precipitation in the biome, allowing researchers to measure the impact of both deforestation and global greenhouse gas emissions on the forest. Deforestation accounts for 74.5% of the reduction in precipitation and 16.5% of the temperature increase in the biome during the dry season.
The researchers divided the biome into 29 analysis blocks, each covering an area of 300 kilometers. These blocks were designed to enable large-scale climate analyses, considering major precipitation events and broader climate systems. Despite this large-scale focus, the study achieved high spatial precision by using vegetation suppression mapping developed by the MapBiomas network; researchers were able to work with data at a resolution of just 30 meters. By cross-referencing this information, they could track how changes in vegetation cover over the decades affected precipitation and temperature in different parts of the region.
In addition to helping understand the process, the research raised another warning signal: maintaining current rates of local deforestation and global greenhouse gas emissions will increase climate extremes in the region, bringing it closer to a critical stress point. This could lead to increasingly severe impacts on the ecological balance as early as 2035. Currently, the average forest cover loss is 19%, but some areas have already reached up to 80% deforested surface.
“The Amazon is a very complex biome that receives moisture from the ocean and has a highly balanced hydrological cycle. It is already being impacted. We need to start reversing this process, and there is no room for additional stress factors in the biome, whether internal or external,” explained Professor Marco Franco from USP’s Institute of Astronomy, lead author of the article published in the journal Nature.
The researchers avoid using the term “tipping point” for the forest, as there is no consensus on its definition in the scientific community. However, they are unequivocal in stating that there is no safety margin for continued exploitation in the region. Large ventures, such as mines and thermoelectric plants, could further destabilize the environment and have the potential to affect vast areas.
Drought
According to Marco Franco, the drought “is increasing by an average of 12 days every 10 years.” The effects are already felt with a relatively small vegetation loss – just a 10% reduction in the analyzed areas. The data show that suppression rates between 10% and 40% of native vegetation lead to a sharper drop in precipitation and further intensify local temperature increases.
Understanding this impact, the participants warn, highlights both the responsibility and the potential for cooperation between governments.
“We already knew that climate change was happening, based on previous studies. Now, we can measure it – and that allows us to sit at the table and talk with those responsible. It helps understand our role – Brazil’s role – regarding deforestation, and to dialogue with the rest of the world about the impact of global greenhouse gas emissions on the forest,” explained Professor Luiz Machado, who coordinated the study.
Regarding the research findings, precipitation during the dry season decreased by about 21 millimeters per year, with deforestation accounting for 15.8 mm of that reduction. The maximum temperature rose approximately 2 °C, with 16.5% of the increase attributed to forest loss and the rest to global climate change.
This impact, however, varies by region. In areas of the eastern Amazon where vegetation cover remains close to its original state – with suppression below 10% – the drought effects are much less severe. In these regions, the temperature increase is attributed almost entirely to industrial emissions from external sources, particularly from Global North countries like the United States and China. In contrast, in the southeastern parts of the biome – such as the Santarém region in the state of Pará – the impact of deforestation on temperature increase is more balanced, and the drought effects are significantly more intense, Franco explained.
In the article, the researchers warn that if deforestation continues unchecked, the results suggest an additional drop in total precipitation during the dry season and a greater temperature increase.
Challenge
The group’s next challenge is to assess the potential impact on the forest under different scenarios up to the year 2100. One of their main contributions, besides establishing the relationship between deforestation, precipitation, and temperature increases, is making their parameters available to other research groups – allowing, for example, biologists to use the data to study effects on species and more localized areas in the biome.
The Brazilian Amazon lost 14% of its native vegetation between 1985 and 2023, according to MapBiomas data, totaling 553,000 km² – an area equivalent to the territory of France. The expansion of pastures was the main driver of this loss during that period. Although the deforested area has decreased in the last two years, fires and the expansion of agricultural land continue to threaten the region.